Isoxaflutole, known by the chemical name 5-cyclopropyl-4-[2-methylsulfonyl-4-(trifluoromethyl)benzoyl]isoxazole, is represented by the following structural formula I:

Isoxaflutole is a p-hydroxyphenyl pyruvate dioxygenase inhibitor. This enzyme converts p-hydroxyphenyl pyruvate to homogentisate, a key step in plastoquinone biosynthesis. Inhibition of this enzyme leads to indirect inhibition of carotenoid biosynthesis, giving rise to chlorosis of new growth.
Isoxaflutole was first reported by B. M. Luscombe et al. (Proc. Br. Crop Prot. Conf.—Weeds, 1995, 1, 35).
The oxidation of (5-cyclopropyl-4-isoxazolyl)[2-(methylthio)-4-(trifluoromethyl)phenyl]-methanone of formula (II) to isoxaflutole of formula (I) by reaction with chloroperbenzoic acid is disclosed both in U.S. patent applications Nos. 2005288516 and 2003055292. Such synthesis method has disadvantages both in term of yield and cost and, therefore, is not applicable for large scale production.

The oxidation of sulphenyl phenyl-substituted isoxazoles derivatives generally according to U.S. Pat. No. 5,747,424 is conducted using hydrogen peroxide, acetic anhydride and acetic acid or chloroperbenzoic acid in dichloromethane. However, no specific example for producing isoxaflutole is disclosed.
It would be highly desirable to have an improved process for the production of isoxaflutole which is suitable for industrial use, highly efficient, low-cost, environmentally friendly, and provides a high yield in a short reaction time, thereby overcoming the deficiencies of the prior art. The present subject matter provides such a process.